Pitot tube flow sensors of the type disclosed in U.S. Pat. No. 4,559,836 to Darrel F. Coleman et al. have been in use for many years in differential pressure flow measurement systems. Such systems detect the average fluid impact, or high, pressure exerted on the upstream facing side of the pitot tube and detect the low fluid pressure on the downstream facing side of the tube. Traditionally, the high and low fluid pressures have been applied to a pressure transducer in order to derive an electrical signal representative of the differential pressure. By known mathematical relationships, the differential pressure is converted to a fluid flow rate.
The fluid pressures sensed and conveyed by the pitot tube or other kind of differential pressure sensor, such as an orifice plate, for example, are conveyed to the pressure transducer through an interconnecting head, such as the one shown by reference numeral 24 in the said '836 U.S. Patent, or by a valve manifold, such as the one shown by reference numeral 17 in U.S. Pat. No. 4,466,290 to Roger L. Frick.
When it is desired to sense the temperature of the medium flowing in the pipe, temperature sensing devices such as a Thermowell RTD (Resistive Temperature Device) have been used, inserting the RTD into a protective sheath, such as a "Thermowell", which is immersed in the fluid whose temperature is being sensed. Typically, the temperature sensor is introduced into the flowing fluid at a location separate from that of the flow rate sensor, creating additional problems associated with opening and then sealing the conduit wall around anything inserted therein.
In the continued development of sophisticated flow measurement systems for process fluids it has become increasingly important to be able to measure the volume and mass of the fluid, as well as its flow rate. In order to do that, however, temperature of the fluid must be known. Because the intrusive measurement of various parameters of a fluid flowing in a pipe requires penetration of the pipe, it becomes increasingly important to sense the required parameters with a single instrument, requiring only one intrusion into the pipe.
It is therefore, the primary aspect of the present invention to provide a single apparatus for sensing the temperature of a fluid flowing in a confined channel (a pipe, for example), as well as determining the differential pressure that is detected by a rate of flow sensor.
A second object of the invention is to provide a combination temperature and pressure sensing device for fluid flowing in a pipe that will allow the temperature sensing portion of the assembly to be removed and replaced without having to also remove the differential pressure sensor from the pipe.
Another aspect of the present invention is to advantageously use the available space inside of a prior art pitot tube to house a temperature-sensing device.
A still further object of the present invention is to utilize a pitot tube type of sensor body as the carrier of a temperature sensor within the conduit carrying the flowing fluid.
And a still further object of the present invention is to provide temperature sensing of the fluid contained within a fluid flowmeter assembly, whether within the primary fluid carrying conduit or within some portion of the assembly that is exterior to the conduit.
Other and further objects, features and advantages of the invention will become apparent upon a reading of the detailed description of a preferred form of the present invention.